ACCUNET.RTM. switched 384 and 1536 digital data services available from AT&T, and other similar services available from other inter-exchange telecommunications carriers, are usage-sensitive dial-up digital data services capable of transporting 384 Kbps and 1.536 Mbps rate data between customer presses locations. These offerings are well suited for such dial-up, i.e., on-demand, high speed data transmission applications, as bulk data transfer, computer graphics, enhanced teleconferencing, video communications, computer aided design, image transfer and retrieval, and so on.
Currently, customers obtain access/egress to the above-described transport services by, for example, using private lines between the customer presses and the inter-exchange carrier location. In a common arrangement, access is provided via the ACCUNET.RTM. T1.5 service (also known as T1 service), which includes 1.544 Mbps digital private lines that are available from AT&T, and that use Primary Rate Interface (PRI) signaling. These private lines connect a toll switch (for example, a 4ESS.TM. switch that supports Integrated Services Digital Network (ISDN) interface standards, with Customer Premises Equipment (CPE) that also supports the ISDN protocol.
While the foregoing arrangement is satisfactory for some customers, it has some drawbacks, notably cost. In particular, in order to advise the ISDN switch of information needed for routing, it is necessary for the customer to have interface equipment, generally known as a D-channel controller (DCC), to generate ISDN signaling messages based upon customer defined call set-up parameters. However, many customers cannot presently afford to obtain the advantages associated with ISDN service, since the cost of a D-channel controller and a D-channel is prohibitively high.
In addition, the present arrangement is inefficient, because, in order to obtain ISDN 1.536 Mbps functionality, a minimum of two 1.544 Mbps T1 transmission lines are presently required. More specifically, a T1 line has, in reality, somewhat less than 1.544 Mbps transmission capability, because of signaling overhead. Even if the full 1.544 Mbps capacity were available, it would not be enough: the ISDN format requires a 1.536 Mbps transmission channel, plus a 64 Kbps signaling channel, adding up to more than the T1 capability. If two T1 lines are used for only one ISDN link, the excess capacity (approximately 1.480 Mbps) is essentially wasted.